Transportation vehicles which operate on gasoline-powered internal combustion engines have been the source of many environmental problems. The output products of internal combustion engines cause, for example, smog and other exhaust gas-related problems. Various pollution control measures minimize the amount of certain undesired exhaust gas components. The process of burning, however, inherently produces some exhaust gases.
Even if the exhaust gases could be made totally benign, however, the gasoline based internal combustion engine still relies on non-renewable fossil fuels.
Many groups have searched for an adequate solution to the energy problems.
One possible solution has been fuel cells. Fuel cells chemically react using energy from a renewable fuel material. Methanol, for example, is a completely renewable resource. Moreover, fuel cells use an oxidation/reduction reaction instead of a burning reaction. The end products from the fuel cell reaction are typically mostly carbon dioxide and water.
Some previous methanol fuel cells used a "reformer" to convert the methanol to H.sub.2 gas for a fuel cell. Methanol fuel cells used a strong acid electrolyte. The present inventors first proposed techniques which would allow a fuel cell to operate directly from methanol and without an acid electrolyte--a direct feed fuel cell. The subject matter of this improvement is described in our U.S. Pat. No. 5,599,638, the disclosure of which is herewith incorporated by reference to the extent necessary for proper understanding. Since this is the work of the present inventors, of course, there is no admission made here that this patent constitutes prior art against the present invention.
The subject matter of the present invention describes further refinements of such a direct fed fuel cell. Various improvements to the fuel cell structure itself are described herein, based on the inventors' further work on this concept. These improvements include improved formulations for the electrode which improve its operation.
The electrode operation includes an improved catalyst, which improves the efficiency of methanol production. Fuel cells use an expensive platinum catalyst. The electrode formulations given herein define techniques which reduce or obviate the need for the platinum catalyst.
Techniques for forming the cathode electrode are also described herein. These techniques optimize the operation of the cathode for use with non-pressurized air. This even further improves the efficiency of the fuel cell by allowing ambient temperature and atmospheric pressure air as the reduction mechanism.
Formation techniques for the electrodes are also described, including techniques to condition the membrane. A formation of a particularly preferred membrane electrode assembly is also defined. The present invention also defines flow field designs which facilitate supplying the liquid fuel to the catalyst.
The fuel cell system eventually needs to be used in a final product. This final product could be an internal combustion engine or could be much simpler electronic devices, such as a radio. Any electrically-driven product could operate based on electrical power produced from these fuel cells. The inventors of the present invention have discovered certain techniques to improve the operation and ameliorate these problems which might otherwise exist.
The techniques of the present invention also enable a "system operation" by describing techniques to operate the fuel cell as part of an overall system.
These system techniques includes sensors for measuring methanol concentration and other important parameters. The inventors realized that various sensors for various parameters would be necessary. The inventors could not find a commercial sensor. The present invention describes a way of modifying the techniques which they use in their fuel cell to form a sensor. This sensor operates with high reliability using the techniques of this fuel cell.
Another technique defines formation of monopolar cells.